ASRJC 2021 J2Prelims H2Chem P3 QP

ASRJC JC2 PRELIMS 2021 9729/03/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2021 JC 2 PRELIMINARY EXAMINATION NAME:_________________________________ ( ) CLASS: 21 /____ CHEMISTRY 9729/03 Paper 3 Free Response 20 September 2021 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and register number in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions Section B Answer one question A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Paper 3 A1 /19 Paper 1 (15%) / 30 A2 /18 Paper 2 (30%) / 75 A3 /19 Paper 3 (35%) / 76 B4* /20 Paper 4 (20%) / 55 B5* /20 Percentage *Circle the question you have attempted Grade This document consists of 28 printed pages.

2 ASRJC JC2 PRELIMS 2021 9729/03/H2 Section A Answer all the questions from this section. 1 (a) SiH4, PH3 and H2S are three compounds whose central atoms in their molecules are elements in Period 3 of the Periodic Table. (i) State and explain the bond angles in the molecules of these three compounds. [4] (ii) In this question, you may assume that phosphorus and hydrogen have the same electronegativity. Draw the three molecules, SiH4, PH3 and H2S and indicate for each one the polarity of each of the bonds it contains and the overall polarity of the molecule. [4] (iii) State the properties of a gas necessary for it to approach ideal behavior. [2] (iv) Of the three gases at 400 K, the behaviour of SiH4 is closest to ideal gas behavior. Suggest why H2S deviate more from ideal behaviour than SiH4. [1] …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ………………………………………………………………………………………………….

3 ASRJC JC2 PRELIMS 2021 9729/03/H2 [Turn over …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ………………………………………………………………………………………………….

4 ASRJC JC2 PRELIMS 2021 9729/03/H2 (b) (i) Define the term lattice energy. [1] (ii) Use the data in Table 1.1, together with relevant data from the Data Booklet, to calculate a value for the lattice energy of magnesium iodide, MgI2(s). Show your working. Table 1.1 value / kJ mol–1 electron affinity of iodine, I(g) + e– ® I–(g) –295.4 enthalpy change of sublimation of iodine molecules, I2(s) ® I2(g) +62.4 standard enthalpy change of atomisation of Mg(s) +148 standard enthalpy change of formation of MgI2(s) –364 [3] …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ………………………………………………………………………………………………….

5 ASRJC JC2 PRELIMS 2021 9729/03/H2 [Turn over (c) Magnesium forms an important group of covalent compounds which are known as Grignard reagents. Many Grignard reagents, with different alkyl or aryl groups, have now been prepared and are widely used in organic synthesis. A typical example of the use of a Grignard reagent is the two–step reaction of C2H5MgBr with propanone, CH3COCH3 to form 2–methylbutan–2–ol. (i) Suggest the type of reaction which occurs in step 2. [1] (ii) Suggest the structural formula of the final organic product formed when is reacted with ethanal, CH3CHO, in a similar two–step process. [1] (iii) The Grignard reagent CH3CH2MgBr can be readily converted into a carboxylic acid by using carbon dioxide, as shown in the two–step reaction sequence in Fig. 1.1. Fig. 1.1 Suggest the structural formula for compounds A and B. [2] …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. C2H5MgBr + CH3COCH3 step 1 CH3C OMgBr CH3 C2H5 step 2CH3CCH3 + Mg(OH)Br C2H5 OH MgBr CH3CH2MgBr + CO2 step 1 step 2 compound A compound B + Mg(OH)Br

6 ASRJC JC2 PRELIMS 2021 9729/03/H2 (d) Two different complexes F and G can be obtained by reacting aqueous cobalt(III) chloride with ammonia under various conditions. Each complex contains a cobalt(III) ion bonded to six ligands, which can be either NH3 or Cl–. The cobalt(III) complexes in F and G are octahedral in shape and an octahedral arrangement is shown in Fig. 1.2. Fig